Power charges or power cartridges are used in oil and gas well setting tools for igniting and burning to power the setting of downhole tools such as plugs, packers, cement retainers, and other devices in well casing. Power charges are constructed of propellant mixtures composed of carefully controlled combustible elements containing an oxidizer which when ignited will begin a slow burn lasting approximately thirty seconds. The gas derived from a burning power charge propellant mixture gradually builds up to high pressures and causes a setting tool to stroke, setting a downhole tool in a well. In conventional setting tools, the power charge is placed in a power charge chamber which also provides a combustion chamber. The power charge is burned and typically creates gas pressure from 7,000 psi to 13,000 psi. Typical prior art power charges were made by packing the propellant into a sleeve formed of plastic, fiberglass or steel. Some prior at power charges have a first end which is open and which exposes the combustible material to an igniter. Other power charges have an igniter embedded in the first end of the power charge.
Problems have been encountered when the fiber glass and the plastic sleeves are used as power charge housings. Burning the power charges will often create plastic debris which has blocked flow ports and caused the setting tools to fail to operate properly. Also, partially melted plastic residue will often line the sidewalls of the setting tool power charge combustion chamber and can be difficult to clean from the sidewalls. Steel tubes have also been used for power charge housings, but these also have difficulty. The steel tubes can deform when the flammable mixture of the power charge burns and be difficult to remove from power charge chambers of setting tools. Additionally, steel tubes, plastic tubes and fiberglass tubes can contain the gasses of the power charge mixture as is burns until high pressures build up within the housing, which can lead to an explosive discharge and the tubes being ejected as a projectile from a burning fire. This has resulted in the Department of Transportation to classifying power charges as explosives when the power charges have outer housings provided by steel tubes, fiberglass tubes, and plastic tubes.
Some prior art power charges have an igniter located in one end, embedded in the propellant. Prior art power charges are typically cylindrical. Shipping and handling, variations in temperature, and shrinkage of propellant mixtures with variations in humidity can cause the igniter to become loose in the propellant mixture, with some having completely fallen out of the power charge housing. Although the power charge igniter may be pushed back into the propellant mixture by hand, the igniter will remain susceptible to being jostled and disconnecting from with the power charge propellant material. This condition is not acceptable.